Dog Keeps Pooping on Beds?

My dog is 4 this year and is well trained. She is very needy and spoiled, but can also handle discipline. The past couple of days she's been left for literally an hour maybe a little longer and she has managing to pull the stair gate open and deciding to poo on beds. Which is strange as I know she peed on my bed when we 1st moved, but I have a new bed duvet and mattress since. Next day, I make sure my door is shut and the gate is closed and my parents come home to see she has done the same to my brother's bed.

She spends most of her day outside as well as being taken for a walk every evening so she had plenty of time to do her nasties. I didn't mind when she was a puppy, but she's almost 4 so it's very odd.

I know my dog doesn't like change because she will only do something this outrageous when shes trying to get our attention. We bought some chickens a few weeks ago, but she's use to them now and will happily leave them be. The past few days she has had to be left, but as I said only for an hour to two hours. We've done this in several homes before, so I am a little confused as go why she would do this 2 days in a row especially after she was told off by myself and summoned to her bed for the rest of the evening.

Is she ill or just in desperate need for attention?
I'm very frustrated with her, but also concerned as even if she has been locked in the house she knows how to open the back door. And surely a dog that knows it's not allowed upstairs would just do the obvious thing if it was desperate and just do somewhere down stairs or do it on the floor instead of a bed.

Help?

By H